Process for producing spherical metal-oxide powder particles

Abstract

There is a process for producing spherical metal-oxide powder particles. They are used as finely ground raw and filler materials in mineral, ceramic and refractory construction, technical and auxiliary materials, as well as for polishing and grinding agents.

What is claimed is: 
     
       1. Process for producing spherically shaped metal-oxide powder particles comprising the steps of (a) reducing aluminum oxide and at least one metal oxide selected from the group consisting of SiO 2 , MgO and CaO thermally and evaporating to produce evaporated products;   (b) oxidizing the evaporated products by mixing with air or oxygen in a gas stream, and condensing as melt particles;   (c) cooling the melt particles further in the gas stream and solidifying to form metal-oxide powder particles; and   (d) separating the powder particles from the gas stream via a dust filter.   
     
     
       2. Process according to claim 1, comprising providing an open submerged electric arc furnace for the evaporation; and in said furnace a metered admixturing of oxidizing gases, inert gases and ambient air takes place via an exhaust suction system of the furnace.   
     
     
       3. Process according to claim 1, comprising providing petroleum coke in the thermal reduction as a carbon vehicle, in an amount of 15% to 30% by weight based on an amount of materials charged.   
     
     
       4. Process according to claim 2, wherein following the mixing with air or oxygen, the gas stream has a concentration of metal-oxide particles less than 20 g/Nm 3 . 
     
     
       5. Process, according to claim 1, comprising providing ceramic and refractory residual materials as a starting material, and said starting material contains oxides, nitrides, carbides of aluminum and silicon.   
     
     
       6. Process according to claim 5, comprising the residual materials contain metallic aluminum and its alloy components.   
     
     
       7. Process according to claim 5, wherein the residual materials contain free carbon.   
     
     
       8. Process according to claim 5, wherein the residual materials are present in a size of 1 to 50 cm.   
     
     
       9. Process according to claim 1, wherein the residual materials are directly converted into a gas phase without prior crushing.   
     
     
       10. Process according to claim 1, wherein the residual materials are abruptly heated to a temperature of above 2000° C., reduced and evaporated in an arc.   
     
     
       11. Process according to claim 1, wherein oxidizing and condensing of the particles takes place within 0.5 to 2.5 seconds.   
     
     
       12. The process according to claim 1, wherein the spherically shaped metal-oxide powder particles contain from 42% to 85% by weight of Al 2  O 3  ;   from 2% to 55% by weight of SiO 2  ;   from 0.1% to 34% by weight of MgO;   from 0.1% to 31% by weight of CaO;   from 0.1% to 0.7% by weight of Fe 2  O 3  ;   from 0.2% to 0.6% by weight of Na 2  O;   from 0.1% to 0.8% by weight of K 2  O; and   from 0.7% to 2.5% by weight of C, with all percents by weight based upon the total particle composition weight.